The Law of Conservation of Matter states that matter cannot be created or destroyed, so why did our experiment lose mass? This mini-unit challenges students to use a model to solve that very problem. Students meet the problem by either conducting their own experiment or viewing a teacher demonstration where the results of a chemical reaction appear to break the Law of Conservation of Matter. After giving them some clues and guiding them to learn about atoms, molecules and chemical equations the students will build models out of whatever materials are available in order to find the missing molecule and learn why the reaction lost mass. Watch as students learn to love hands on real science with the Next Generation Science Standards! Includes a rubric for assessing models that does not limit creativity!